1. Field of the Invention
The present invention is directed to a thermal expansion driven indentation system which allows for controlled application of reproducible precise and continuous loads for the production of stress-strain information. The continuous indentation system in accordance with the present invention adapts well to the generation of load versus penetration depth plots during hardness testing. Continuous indentation tests on high strength steel reveals very close comparisons with conventional fixed load Rockwell test results, and tensile test results.
2. Background of the Discussion
Conventional fixed load hardness tests (i.e. Rockwell, Birnell, etc.) do not provide measurements of well defined material properties. The values generated by these tests only supply relative information about a material's resistance to indentation and/or an indication of the specimen's heat treatment. Further, elastic material which surrounds the plastic zone of the indentation acts to hinder plastic flow. Exploring the combined elastic and plastic deformation behavior during hardness testing would allow for the deduction of the elastic contribution to the final plastic indentation. Thus, useful information can be resolved from hardness testing if load and penetration depth are continuously monitored during indentation. Previous working systems in this area have employed an Instron testing machine (with modified grips) to generate stress-strain relationships of various materials. While promising results have been obtained, machine compliance became a problem when reaching higher loads. Thus, it has become desirable to develope a device which is suited for the application of continuous and precise loads to finally generate a stress-strain relationship.